Field emission cathodes are electron emitting devices which are used, for example, in flat panel displays. A field emission cathode or "field emitter" emits electrons when subjected to an electric field of sufficient strength and appropriate polarity. A side sectional view depicting conventional steps used to manufacture a field emission cathode is shown in Prior Art FIG. 1A. More specifically, in Prior Art FIG. 1A, a first conductive layer or "row electrode" 102 has a resistive layer 104 disposed thereon. An inter-metal dielectric layer 106 disposed above resistive layer 104 has a cavity 108 formed therein. As shown in Prior Art FIG. 1A, a second conductive layer or gate electrode 110 resides above inter-metal dielectric layer 106. A hole or opening 112 is formed through gate electrode 110 directly above cavity 108. Opening 112 is used to form the field emitter which will reside within cavity 108. Typically, the formation of the field emitter is accomplished, in part, using a lift-off or "parting layer", and a closure layer. Unfortunately, conventional lift-off and closure layer deposition and removal methods have severe drawbacks associated therewith.
With reference next to Prior Art FIG. 1B, a side sectional view illustrating the deposition of a lift-off layer 114 is shown. Lift-off layer 114 is formed using an angled physical vapor deposition of, for example, aluminum. Arrows 118 illustrate the angled nature of the deposition of lift-off layer 114. The angled deposition of lift-off layer 114 is required to insure that no lift-off layer material, i.e. aluminum, is deposited into the bottom of cavity 108. As shown in Prior Art FIG. 1B, however, some lift-off layer material 115 may be deleteriously deposited along the sides defining cavity 108. In order to achieve an angled deposition, the entire field emitter structure must be rotated during the deposition of lift-off layer 114. As a result, considerable difficulty, expense, and complexity is introduced into the field emitter structure manufacturing process. Also, lift-off layer 114 must have uniform thickness across the surface of gate electrode 110. This additional requirement of uniformity further complicates the lift-off deposition process.
With reference still to Prior Art FIG. 1B, lift-off layer 114 has another substantial disadvantage associated therewith. Specifically, lift-off layer 114 reduces the opening above cavity 108. That is, lift-off layer 114 attaches to the inner diameter of opening 112 in gate electrode 110. As a result, the diameter of opening 112 is effectively reduced. Hence, the opening above cavity 108 is limited to the diameter of opening 116 in lift-off layer 114. Therefore, the diameter of opening 112 in gate electrode 110 must be increased to insure that the final diameter (i.e. the diameter of opening 116 in lift-off layer 114) is as large as is desired. It is well known, however, that increasing the diameter of opening 112 in gate electrode 110 can reduce the performance characteristics of the field emitter structure.
Referring next to Prior Art FIG. 1C, a side sectional view illustrating the initial formation of a closure layer 118 is shown. Closure layer 118 is comprised of electron emissive material such as, for example, molybdenum. The electron emissive material which forms closure layer 118 is also deposited into cavity 108 as shown by structure 120. Typically, the electron emissive material is deposited using, for example, an e-beam evaporative deposition method.
Referring now to Prior Art FIG. 1D, a side sectional view illustrating a completed deposition of electron emissive material is shown. As shown in Prior Art FIG. 1D, closure layer 118 completely seals cavity 108. Additionally, as the electron emissive material is deposited as shown in Prior Art FIGS. 1C and 1D, an electron emitting structure 120 commonly referred to as a "Spindt-type" emitter is formed within cavity 108 (Spindt-type emitters are described in detail in U.S. Pat. No. 3,665,241 to Spindt et al. which is incorporated herein by reference as background material). After Spindt-type emitter 120 is formed, closure layer 118 must be removed.
With reference now to Prior Art FIG. 1E, a side sectional view illustrating the removal of closure layer 118 is shown. When removing closure layer 118, care must be taken not to damage or otherwise adversely affect Spindt-type emitter 120. Such a removal process is further complicated by the fact that both closure layer 118 and Spindt-type emitter 120 are formed of the same electron emissive material. Prior art techniques remove closure layer 118 by etching lift-off layer 114 using an etchant which attacks the aluminum lift-off layer 114. As a result, lift-off layer 114 "lifts" from underlying gate electrode 110 and, consequently, removes closure layer 118, as illustrated in Prior Art FIG. 1E. Prior art lift-off layer etchants do not, however, attack the electron emissive material of either closure layer 118 or Spindt-type field emitter 120. Unfortunately, such a lift-off process results in the generation of flakes or contaminating chunks, typically shown as 122a-122c, which contaminate the etchant. Flakes or chunks 122a-122c can also redeposit within cavity 108, as shown by chunk 122c, and compromise the integrity of Spindt-type emitter 120 formed therein. As a result, the Spindt-type emitter can be severely damaged or even shorted to gate electrode 110. Hence, prior art "lift-off" closure layer removal methods include deleterious side effects.
Thus, a need exists for a closure layer deposition and removal method which eliminates the need for a complex and difficult to manufacture lift-off layer. A further need exists for a closure layer deposition and removal method which does not substantially limit gate electrode hole diameter. Yet another need exists for a closure layer deposition and removal method which reduces deleterious redeposition of portions of the closure layer within the emitter cavity.